# # Program information file # PROGRAM_ID 2024B033 PROGRAM_TITLE SpeX Observations of Kilonovae in the Fourth LIGO/Virgo Observing Run PROGRAM_INV1 Ashley Villar PROGRAM_INV2 Conor Ransome PROGRAM_INV3 Alexander Gagliano PROGRAM_INV4 Edo Berger PROGRAM_INV5 Karthik Yadavalli PROGRAM_SCICAT extra-galactic PROGRAM_ABSTRACT_BEG We propose to use SpeX on IRTF to observe two EM counterparts to neutron star mergers observed during the second part of LIGO/Virgo's fourth observing run, which will begin in April 2024 and will last for 10 months. A kilonova refers to the thermal explosion following a neutron star merger that results from the radioactive decay of newly synthesized, heavy ['r-process'] elements. The NIR emission of kilonova is of particular interest, due to the expected signatures of the heaviest elements [lanthanides and actinides] at these wavelengths. With an increased sensitivity, LIGO/Virgo is expected to discover ~1 KN observable to IRTF. We request three observations of one potential event, spread across 3-6 nights, depending on observability. Our ultimate aim is to take the earliest NIR spectrum of a localized kilonova and to uncover the intrinsic diversity of these newly discovered events. PROGRAM_ABSTRACT_END